Error correction of system transfer function by use of input compensation

Abstract

A technique to modify the input data to any system so as to cancel errors in the transfer function of that system. The system error response to each possible input amplitude transition is determined. A compensating input sequence is calculated which compensates for this error. The error-correcting sequence is stored in memory for each possible transition. These pattern sequences exactly cancel errors in the response to each of the possible, individual sample-to-sample transitions. For each of any series of input data sample transitions, the appropriate correction sequence is recalled from memory. The composite corrected input is the sum of Y correction sequences from Y preceding sample transitions.

What is claimed is: 
     
       1. A compensator for modifying the input signal to a system, wherein said input signal is a time varying series of digital samples, so as to cancel errors in the transfer function of the system, comprising: a register responsive to the input signal and clocked by a system clock to provide a register output representative of a prior input data sample;   an input compensation algorithm apparatus responsive to a current input data sample and to the register output to provide a sequence of corrected input data values which cancel errors in the transfer function of the system, said sequence of corrected input data values dependent on the difference between the current input data sample and the prior input data sample and extending through a sufficient period of time to cancel errors in the said transfer function of said system, said sequence of corrected input data values for application to the system.   
     
     
       2. The compensator of claim 1 wherein the input compensation algorithm apparatus includes a digital memory apparatus for storing digital compensation values to be accessed in response to said transition value. 
     
     
       3. The compensator of claim 1 wherein said sufficient period of time extends over Y data sample periods, and said algorithm apparatus includes: a chain of Y-1 serially connected data registers, so as to produce Y-1 sets of stored data samples, a first register having as its inputs said current data sample and said prior data sample, wherein each data set is a set of a current data sample and a corresponding prior data sample for the Y-1 immediately prior samples;   Y digital memory lookup tables, a first table for producing a first sample of a synthesized input sequence corresponding to said current data sample and said prior data sample, and the remaining Y-1 tables each for producing a corresponding sample of said synthesized input sequence corresponding to one of said set of stored data samples for a prior sample period, thereby producing a synthesized input sequence of Y samples;   a summing apparatus for summing said Y samples to produce said corrected input data value.   
     
     
       4. The compensator of claim 1 wherein said sufficient period of time extends over Y data sample periods, and said algorithm apparatus includes: a differentiator responsive to said current data sample and said prior data sample for producing a differentiated sample value representative of the difference between said current data sample and said prior data sample;   a chain of Y-1 serially connected data registers, so as to produce Y-1 stored data samples, a first register having as its input said differentiated sample value, wherein each stored data sample is a differentiated sample value for a prior current data sample and a corresponding prior data sample for the Y-1 immediately prior samples;   Y digital memory lookup tables, a first table for producing a first sample of a synthesized input sequence corresponding to said differentiated data value, and the remaining Y-1 tables each for producing a corresponding sample of said synthesized input sequence corresponding to one of said stored differentiated data samples for a prior sample period, thereby producing a synthesized input sequence of Y samples;   a summing apparatus for summing said Y samples to produce a summed value; and   an integrator for summing said summed value for each of Y sample periods to produce said corrected digitized input data value.   
     
     
       5. A method for correcting errors in the transfer function of an electronic system which operates on time-sampled, digital input signals, comprising a sequence of the following steps: storing for one sample period a current data sample to provide a prior input data sample for an immediately prior sample period; and   processing the current data sample and the prior input data sample to determine a sequence of corrected input data values, said sequence of corrected input data values dependent on the difference between the current data sample and the prior data sample and extending through a sufficient period of time to cancel errors in the said transfer function of said system, said sequence of corrected input data values for application to the system.   
     
     
       6. The method of claim 5 wherein said sufficient period of time extends over Y data sample periods, and further includes the steps of: storing Y-1 sets of stored data samples, wherein each data set is a set of a current data sample and a corresponding prior data sample for the Y-1 immediately prior samples;   using Y digital memory lookup tables, including a first table for producing a first sample of a synthesized input sequence corresponding to said current data sample and said prior data sample, and the remaining Y-1 tables each for producing a corresponding sample of said synthesized input sequence corresponding to one of said set of stored data samples for a prior sample period, thereby producing a synthesized input sequence of Y samples;   summing said Y samples to produce said corrected input data value.   
     
     
       7. The method of claim 5 wherein said sufficient period of time extends over Y data sample periods, and said method includes: differentiating said current data sample and said prior data sample to produce a differentiated sample value representative of the difference between said current data sample and said prior data sample;   storing Y-1 stored differentiated sample values for the Y-1 immediately prior samples;   using Y digital memory lookup tables, a first table for producing a first sample of a synthesized input sequence corresponding to said differentiated data value, and the remaining Y-1 tables each for producing a corresponding sample of said synthesized input sequence corresponding to one of said stored data samples for a prior sample period, thereby producing a synthesized input sequence of Y samples;   summing said Y samples to produce a summed value; and   integrating said summed value for each of Y sample periods to produce said corrected input data value.   
     
     
       8. A compensator for modifying the input signal to a system so as to cancel errors in the transfer flnction of the system, wherein the input signal is a time varying analog signal, comprising: sampling apparatus for periodically sampling the input signal, said sampling apparatus clocked by a sample clock;   an analog-to-digital converter (ADC) for converting the input data samples to a digitized current sample representation;   a register connected to the ADC output and clocked by the sample clock to provide a register output representative of a prior digitized input data sample;   an input compensation algorithm apparatus connected to the ADC output and the register output to provide a sequence of corrected digitized input data values in response to the current sample representation and the prior input data sample, said sequence of corrected input data values dependent on the difference between the current sample representation and the prior sample representation and extending through a sufficient period of time to cancel errors in said transfer function of said system;   digital-to-analog converter (DAC) apparatus for converting the sequence of corrected input data values to a sequence of corrected analog data values for application to the system.   
     
     
       9. The compensator of claim 8 wherein the input compensation algorithm apparatus includes a digital memory apparatus for storing digital compensation values to be accessed in response to said transition value. 
     
     
       10. The compensator of claim 8 wherein said sufficient period of time extends over Y data sample periods, and algorithm apparatus includes: a chain of Y-1 serially connected data registers, so as to produce Y-1 sets of stored data samples, a first register having as its inputs said current data sample and said prior data sample, wherein each data set is a set of a current data sample and a corresponding prior data sample for the Y-1 immediately prior samples taken by the ADC;   Y digital memory lookup tables, a first table for producing a first sample of a synthesized input sequence corresponding to said digitized current data sample and said digitized prior data sample, and the remaining Y-1 tables each for producing a corresponding sample of said synthesized input sequence corresponding to one of said set of stored data samples for a prior sample period, thereby producing a synthesized input sequence of Y samples;   a summing apparatus for summing said Y samples to produce said corrected digitized input data value.   
     
     
       11. The compensator of claim 8 wherein said sufficient period of time extends over Y data sample periods, and said algorithm apparatus includes: a differentiator responsive to said digitized current data sample and said digitized prior data sample for producing a differentiated sample value representative of the difference between said current data sample and said prior data sample;   a chain of Y-1 serially connected data registers, so as to produce Y-1 stored data samples, a first register having as its input said differentiated sample value, wherein each stored data sample is a differentiated sample value for a prior current data sample and a corresponding prior data sample for the Y-1 immediately prior samples taken by the ADC;   Y digital memory lookup tables, a first table for producing a first sample of a synthesized input sequence corresponding to said digitized differentiated data value, and the remaining Y-1 tables each for producing a corresponding sample of said synthesized input sequence corresponding to one of said stored differentiated data samples for a prior sample period, thereby producing a synthesized input sequence of Y samples;   a summing apparatus for summing said Y samples to produce a summed value; and   an integrator for summing said summed value for each of Y sample periods to produce said corrected digitized input data value.   
     
     
       12. A method for correcting errors in the transfer function of an electronic system which operates on time varying analog input signals, comprising a sequence of the following steps: periodically sampling the input signal at a rate determined by a sample clock to provide a sampled analog value;   converting the sampled analog value to a digitized current sample representation of a current data sample;   storing for one sample period said current data sample to provide a prior digitized input data sample for an immediately prior sample period;   processing the current sample representation and the prior input data sample to determine a sequence of corrected digitized input data values, said sequence of corrected input data values dependent on the difference between the current sample representation and the prior sample representation and extending through a sufficient period of time to cancel errors in said transfer function of said system; and   converting the corrected input data value for application to the system.   
     
     
       13. The method of claim 12 wherein said sufficient period of time extends over Y data sample periods, and further includes the steps of: storing Y-1 sets of stored data samples, wherein each data set is a set of a current data sample and a corresponding prior data sample for the Y-1 immediately prior samples;   using Y digital memory lookup tables, including a first table for producing a first sample of a synthesized input sequence corresponding to said digitized current data sample and said digitized prior data sample, and the remaining Y-1 tables each for producing a corresponding sample of said synthesized input sequence corresponding to one of said set of stored data samples for a prior sample period, thereby producing a synthesized input sequence of Y samples;   summing said Y samples to produce said corrected digitized input data value.   
     
     
       14. The method of claim 12 wherein said sufficient period of time extends over Y data sample periods, and said method includes: differentiating said digitized current data sample and said digitized prior data sample to produce a differentiated sample value representative of the difference between said current data sample and said prior data sample;   storing Y-1 stored differentiated sample values for the Y-1 immediately prior samples;   using Y digital memory lookup tables, a first table for producing a first sample of a synthesized input sequence corresponding to said digitized differentiated data value, and the remaining Y-1 tables each for producing a corresponding sample of said synthesized input sequence corresponding to one of said stored differentiated data samples for a prior sample period, thereby producing a synthesized input sequence of Y samples;   summing said Y samples to produce a summed value; and   integrating said summed value for each of Y sample periods to produce said corrected digitized input data value.